This invention relates to film punches, e.g. for providing multiple films such as colour separations with punch register after exposure, and particularly for registering multi-colour half-tone separations produced on an electronic film scanner or process camera.
One type of film punch manufactured by the applicants, has an illuminated platform capable of accepting a maximum film size of 60.times.50 cm and punching heads which are inverted for operation from below upwards. A key film, usually that representing the blue separation or that with the most detail, is selected and placed on the platform over the punching heads, which are operated to perforate the film. The punching heads are brought to a position in which the punches project into, and are retained within the thickness of the key film to provide a positive location. Then the next separation is placed over the key film, slid over the punching heads, registered visually to the key film and the punching heads are operated to perforate the second film. The second separation is removed and the same procedure is repeated for the remaining colour separations, after which the key film is released by depressing the punching heads to their original position.
Early electronic scanners were mostly single-channel and produced colour separations one colour at a time, so that colour sets could be produced in register much the same as on a camera, by fitting the film drum with register pins. This enabled four separate pieces of film to be punched and placed in turn on the pins on the drum.
However, in the multi-channel scanners now in operation such as a four-channel scanner, the original film transparency is fitted to one drum and the fourcolour separations are produced on a single piece of film. One multi-channel scanner can produce register markings on the film that are in register with each separation. Furthermore, if register markings are included with the original transparency, for example by adhering register crosses thereto, then after the scanning operation they will appear against each separation.
The assignee has, for some years now, been manufacturing an apparatus for punching a plurality of exposed films having co-operating image areas to obtain punch registration, which is disclosed in the specification of its U.K. Pat. No. 2059627B and which comprises a stationary support having a platform for supporting the films to be registered and punched, a plurality of punches mounted to said support so as to be capable of punching each film outside its useable image area, two projection units supported by said support and having portions which extend over the platform, the projection units each comprising a projection screen, an optical means for magnifying an image of a respective area of film when such film is supported on the platform and a projection means for projecting the respective magnified image onto the respective projection screen, and means such as a cushion of air for enabling each of said projection units to be moved independently of the other projection unit with respect to said platform and said punches.
In use of the apparatus with exposed films having co-operating image areas, a first one of the exposed films is located in a position in which it can be punched outside its useable image area, and is punched in its located position, the two projection units are moved independently with respect to the located film and into positions in which two magnified images of portions of the image area, or of register markings on film are projected onto the two screens respectively, a second one of the exposed films is placed on the first film, the second film is moved with respect to the first film until two magnified images of co-operating portions of the image area or of the register markings of the second film are aligned on the screens with the two magnified images or register markings respectively of the first film, to obtain registration of the co-operating image areas of the first and second films, and the second film is punched outside its useable image area, and then removed and the method repeated for any remaining films.
By so projecting the film areas, parallax is eliminated, the operator can see two datum positions at once, operator fatigue is reduced, greater accuracy is achieved due to greater enlargement and speed is increased since one area of the film can be held whilst the second area of film is aligned.
Whilst the optical film punch registration in U.K. Pat. No. 2059627 is suitable for many applications, the optical projection unit assembly is bulky, needs high power illumination in view of the long optical paths and an air pump which is noisy to produce the cushions of air. Moreover, optimum registration of the optical images can still take time and be difficult to achieve, in particular in an industry working with negative film separations as opposed to positive film separations, and because there is a momentary time interval between image registration and punching.
To produce positive film separations from the negatives could be an answer but the expense would be prohibitive and would be against the established modus operandi.